The present invention is related to an object sensing apparatus for sensing an object by employing FM-CW waves.
A radar apparatus capable of switching an FM-CW mode and a CW mode is known from the below-mentioned patent publication 1. In the FM-CW mode, FM-CW waves are transmitted, and the FM-CW waves are produced by increasing/decreasing a frequency of CW waves in a triangular wave form in accordance with a time elapse. In the CW mode, CW waves are transmitted which are not frequency-modulated. This known radar apparatus senses preceding-driven vehicles and the like in the FM-CW mode during normal operation, whereas when the sensing operation as to the preceding-driven vehicles and the like by using the FM-CW mode cannot be carried out since snow and mud are attached, the radar apparatus senses a road surface and objects located on the road side by using the CW mode. Then, when the radar apparatus judges that a sensing operation by using the FM-CM mode can be again carried out based upon a sensing result obtained in the CW mode, the radar apparatus restarts to sense preceding-driven vehicles and the like by using the FM-CW mode.
[Patent Publication 1]
Japanese Patent No. 3488610
On the other hand, in the radar apparatus described in the above-described patent publication 1, while the preceding-driven vehicles and the like are sensed in accordance with the FM-CW mode, when signal levels of reflection waves are lowered, so that the preceding-driven vehicle and the like cannot be sensed, this radar apparatus judges an abnormal condition. However, if the abnormal condition is judged based upon only the signal levels of the reflection waves acquired in the FM-CW mode, then the sufficiently high judging precision can not be obtained. Thus, there are some possibilities that although the sensing function of the FM-CW mode is still left, the radar apparatus judges an abnormal condition, and also, although the sensing function is lost, the radar apparatus judges the normal condition.